pathSum.md

Problem

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

Note: A leaf is a node with no children.

Example:

Given the below binary tree and sum = 22,

      5
     / \
    4   8
   /   / \
  11  13  4
 /  \      \
7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

Solution

Go

package main
type TreeNode struct {
 	Val int
 	Left *TreeNode
 	Right *TreeNode
}

func hasPathSum(root *TreeNode, sum int) bool {
    if root==nil{
        return false
    }
    if root.Left == nil && root.Right == nil{
        return sum==root.Val
    }
    l := hasPathSum(root.Left,sum-root.Val)
    if l {
        return l
    }
    r := hasPathSum(root.Right,sum-root.Val)
    return l || r
}

Python 3

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right
        
class Solution:
    def hasPathSum(self, root: TreeNode, targetSum: int) -> bool:
        if root is None:
            return False
        if root.left is None and root.right is None and targetSum==root.val:
            return True
        
        left_v = self.hasPathSum(root.left,targetSum-root.val)
        if left_v==True:
            return left_v
        right_v = self.hasPathSum(root.right,targetSum-root.val)
        return left_v or right_v